This project is concerned with the study of certain enzymes and other proteins that consist of multiple subunits and that assemble into macromolecular functional units. The glutamate dehydrogenases of vertebrates and of Neurospora crassa are enzymes of diverse properties that are regulated in different ways -the vertebrate ones by allosteric effectors, such as purine nucleoside di- and triphosphates, and those of Neurospora by the level of glutamate in the culture medium. Determination of the amino acid sequences and modification of specific amino acid residues permit the identification of binding sites for substrates, coenzymes and effectors and of residues concerned with assembly into the active enzymes. The flagellins of bacteria and the phycociliproteins of algae represent model organelle systems that consist of one (the former) or two (the latter) types of chains that assemble spontaneously into cellular organelles. Studies on the structure and mode of assembly of these proteins is continuing. Work is beginning on identification of non-histone chromosomal proteins, particularly a nuclear proteinase responsible for histone degradation. BIBLIOGRAPHIC REFERENCES: K.M. Blumenthal and E.L. Smith: Alternative Substrates for Glutamate Dehydrogenases, Biochem. Biophys. Res. Commun. 62, 78 (1975). L. Patthy and E.L. Smith: Reversible Modification of Arginine Residues. Application to Sequence Studies by Restriction of Tryptic Hydrolysis to Lysine Residues, J. Biol. Chem. 250, 557 (1975).